1. Technical Field
The present disclosure relates to laser-driven acceleration systems and more particularly to laser-driven plasma wave electron acceleration systems.
2. Discussion of Related Art
Laser-driven electron acceleration in plasma has become a well-established field since it was proposed several decades ago [1]. In recent years, significant experimental successes have been achieved, including the acceleration of quasi-monoenergetic electron bunches to ˜4 GeV [2] and the generation of MeV-range gamma rays [3]. Typically, these experiments demand laser pulse energies of at least several joules, and consequently existing laser technology limits them to low repetition rates (≤10 Hz).
There are numerous applications for MeV-scale electron beams where a compact and portable high repetition rate source is beneficial, especially for potential scanning purposes and improved data collection statistics. At the low pulse repetition rates of ≤10 Hz, radiography using broadband, moderately divergent laser-plasma-accelerated electron beams from gas jets [4,5], or γ-rays from bremsstrahlung conversion of the beam [6,7] has been demonstrated. Prior work at 0.5 kHz using a continuous flow gas jet has produced ˜100 keV, 10 fC electron bunches [8] and demonstrated their application to electron diffraction experiments [9]. While high repetition rate acceleration of ˜pC electron bunches to MeV-scale using solid and liquid targets has been reported [10,11], gas jet-based laser-plasma electron sources had yet to simultaneously achieve high repetition rate and MeV-scale energies.
In non-plasma based work, time-resolved electron diffraction using laser-driven photocathodes and conventional MeV accelerator structures such as LINACs is an established research area [12], where low emittance and narrow energy spreads are achieved. For <100 fs temporal resolution, that technique requires compensation for space charge effects and timing jitter [12].
The most common and successful laser-plasma-based acceleration scheme is laser wakefield acceleration (LWFA), which can be initiated by relativistic self-focusing of the laser pulse in the plasma. LWFA electron pulses can be ultrashort and are precisely timed to their driving pulses [13]. Relativistic self-focusing has a critical power [14] of Pcr=17.4(Ncr/Ne) GW, where Ne is the plasma density and Ncr is the critical density. As Ncr=1.74×1021 cm−3 for the Ti:Sapphire laser wavelength of λ=800 nm, a very high Ne is needed to keep Pcr well below 1 TW and enable operation with current commercial laser technology for millijoule-scale pulses at 1 kHz.